Drive mechanisms are known that use a planetary gear system driven by a central sun gear. Typically, the central sun gear is coupled to a propulsion unit, like an engine or motor, and the planetary gear system is coupled to an output drive shaft. The sun gear, driven by the propulsion unit, imparts rotation to the drive shaft through the planetary gears.
It is desirable to adjust the speed of the drive shaft without modifying the speed of the propulsion unit. To accomplish this, a ring gear is coupled to the periphery of the planetary gear system. A second propulsion unit imparts rotation to the ring gear concurrent with rotation of the planetary gear system imparted by the main propulsion unit through the sun gear. The concurrent rotation alters the rotational speed of the output drive shaft, while the speed of the main propulsion unit remains constant.
Several independent sets of planetary gears can be used in tandem to impart rotation from a single main propulsion unit to several output drive shafts. A ring gear coupled to one or more of the independent planetary gear sets, can impart a greater speed of rotation to one planetary gear set than to the other, thereby steering the vehicle.
There is a need to axially retain the ring gear in position about the planetary gear set. Typical mechanisms hold the ring gear from moving axially along the drive shaft axis by mechanically mounting the center hub of the ring gear on bearings attached to the drive shaft. This arrangement adds one more mechanical component to the already complex structure of a typical planetary gear system.
There is a need for more compact, less complicated, and lighter weight planetary gear systems. These attributes are important, particularly with respect to smaller, typically battery powered vehicles, like wheelchairs or golf carts or personal mobility scooters.